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DNA EXTRACELLULARE IN SUOLO DI FORESTA MISTA DI FAGGIO-ABETE: DISTRIBUZIONE, EFFETTI E PRODUZIONE
No full textIl Feedback negative pianta suolo (NF) viene definite come lo stabilirsi di condizioni negative per la crescita della pianta indotte da modificazioni del suolo apportate dalla pianta stessa, capaci di modellare la forma della comunità vegetale e la sua diversità. Studi recenti effettuati in condizioni controllate sull’effetto del self-DNA (DNA extracellulare frammentato derivante da lettiera conspecifica) hanno mostrato una nuova possibile spiegazione per il NF specie-specifico, anche se questa ipotesi aspetta ancora di essere verificata in condizioni naturali.
Gli scopi di questa tesi di dottorato sono molteplici e si prefiggono di approfondire la conoscenza della distribuzione del self-DNA in ambienti naturali e di studiarne i suoi effetti in ambiente controllato, con un focus particolare alle foreste di Faggio-Abete del Nord-Est Italia. A questo scopo uno studio di campo e stato portato avanti nel comprensorio forestale dei Laghi di Fusine (UD) basato su approccio basato su metodologia di metabarcoding. Il risultato e osservabile in un chiaro phattern di distribuzione verticale del self-DNA differente tra le due specie target (Faggio ed Abete). Questo può essere spiegato in relazione alla differente qualità della lettiera delle due specie ed alle condizioni ambientali a contorno che possono influenzare diversamente la dinamica di decomposizione nei due diversi tipi forestali.
Da un punto di vista metodologico, il secondo scopo di questa tesi e quello di testare la possibilità di produzione di una grande quantità di self-DNA marcato con isotopi stabili nell’azoto (15N) in modo da poterlo usare in studi successivi per studiare la dinamica di decomposizione. Un protocollo di marcatura basato sull’apporto di una soluzione nutritiva marcata e successivamente un protocollo di estrazione per grandi quantità di materiale vegetali sono stati messi a punto in due studi diversi, uno in camera di crescita su Brassica napus e uno in campo su Fagus sylvatica. Nei due casi i risultati sono stati positivi fornendo importanti informazioni sulla dinamica di marcatura del DNA e permettendo di produrre un grande quantitativo di DNA marcato.
Ultimo scopo di questa tesi e quello di portare un nuovo contributo conoscitivo degli effetti del self-DNA specificatamente in relazione ai sistemi forestali di faggio. Nello specifico, lo scopo e quello di verificare l’effettiva presenza o assenza di NF su plantule di faggio cresciute in mesocosmi in ambiente controllato su differenti tipologie di substrati (Suolo naturale di faggeta, suolo di diversi tipi di lettiera di faggio). Allo scopo di districare i complessi meccanismi esplicativi dei pattern osservati, ogni substrato viene trattato fattorialmente con carbone attivo in modo da verificare un effetto della componente chimica dei substrati oppure sterilizzato per verificare la valenza del microbioma del suolo. Viene aggiunto self-DNA frammentato per verificare il suo possibile effetto negativo. Come risultati si osserva un effetto benefico dovuto al microbioma presente nel suolo di foresta di faggio ed un effetto negativo dovuto alla componente chimica della lettiera. L’aggiunta di self-DNA porta ad un’inibizione quando ci troviamo nelle condizioni più simili all’ambiente di crescita della specie della specie in esame, ovvero sul suolo naturale di foresta di faggio. Tuttavia, chiarire il ruolo funzionale del self-DNA nella già complessa interazione tra effetto mediato dalle caratteristiche della lettiera in interazione con quello mediato dal microbioma sulla crescita dei semenzali richiede ulteriori studi, principalmente per verificare la biodisponibilità del self-DNA sulle differenti matrici utilizzate.Negative plant–soil feedback (NF) is defined as the establishment of negative conditions for plant performance induced in soil by the plants themselves, contributing to shape plant community structure and diversity. The release of toxic compounds from litter decomposition was proposed among the possible causal agents. Recent evidence in controlled conditions of inhibitory effects by self-DNA (i.e. fragmented, extracellular DNA from conspecific litter) provided a suitable explanation for species-specific NF, but such hypothesis awaits to be addressed in natural field conditions. This PhD thesis aims at deepening the knowledge of exDNA distribution and applications in natural environments, with particular focus on natural beech-spruce forest ecosystems. A field study, carried out in the forest system of Fusine Lakes (UD) based on soil DNA metabarcoding approach permitted to demonstrate clear-cut different patterns of vertical distribution for beech exDNA vs. spruce exDNA, as likely related to species-specific differences of litter quality and micro-environmental conditions, both decisively affecting litter decomposition dynamics in the different forest types. Under a methodological perspective, a second aim of this thesis is to test the possibility to produce large amounts of plant DNA labelled with stable isotopes. A simple protocol to label plant material with 15N and subsequent extraction of isotopically labelled DNA was created and tested both in growth chamber controlled condition than in field study. That showed positive results in terms of the level of isotopic signature of both the leaf material and the DNA thereof purified, especially considering the remarkable level of 15N content in the DNA, which shall be used in further studies about exDNA tracking in natural field conditions. A further aim of this thesis is to provide a first contribution specifically referred to beech forest systems. In particular, the occurrence of NF on beech seedlings is tested in a bioassay in microcosms under controlled conditions, considering different species-specific substrate conditioning sources (natural forest soil as well as beech litter amendments). In order to disentangle possible mechanistic explanations of the observed pattern, substrate-dependent effects in the bioassays are factorially combined with substrate treatments intended to either release the possible causal factors of species-specific NF (i.e. substrate microbiome, low molecular weight phytotoxic compounds) or exacerbate the negative effects (i.e. self-DNA addition). As results, a beneficial effect of the home soil microbiome and a detrimental effect of litter chemicals we confirmed for the first time on beech seedlings. The principle of self-DNA inhibition holds also when tested under realistic experimental conditions more similar to natural environment where plants lives. However, clarifying the functional role of self-DNA within the interplay between litter- and rhizosphere-mediated effects requires further investigation, mostly due to a problematic assessment of self-DNA bioavailability in the complex matrix of soil amendments. Besides its relevance for pure knowledge in natural ecosystems, such issue is of foremost importance in the view of self-DNA applications in agro-ecosystems, for the species-specific control of weeds and pathogens
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Melanization in parmelioid lichens as a passive defense mechanism against microbiological degradation
No full textBacterial and Fungal Communities Respond Differently to Changing Soil Properties Along Afforestation Dynamic
Full text linkSpontaneous afforestation following land abandonment has been increasingly recognized as a nature-based solution to mitigate climate change and provide measurable benefits to biodiversity. However, afforestation effects on biodiversity, particularly on soil microbial communities, are still poorly characterized, with most previous studies focusing on artificial plantations rather than forest rewilding dynamics. Here, we assessed changes in topsoil physical-chemical properties and related dynamics of bacterial and fungal community composition and structure following spontaneous afforestation of abandoned grasslands in Northeast Italy over the last 70 years. With a space-for-time approach, we selected four chronosequences representing different successional stages: grassland, early (2000-2020), intermediate (1978-2000), and late (1954-1978). Results showed that spontaneous afforestation progressively reduced topsoil pH and total phosphorus (P), while soil organic carbon (SOC), nitrogen (N), and C:N ratio increased. Correspondingly, the overall α-diversity of the fungal community, assessed by ITS DNA metabarcoding, progressively decreased after an initial increase from grassland conditions, following substrate acidification and trophic specialization. Bacterial diversity, assessed by 16S DNA metabarcoding, was highest at the initial stages, then progressively decreased at later stages, likely limited by lower organic matter quality. Shifts of fungal community composition included an increase of ectomycorrhizal Basidiomycota linked to topsoil's higher SOC, N, and C:N ratio. Differently, bacterial community composition responded substantially to pH, with topsoil acidity favoring Proteobacteria (Pseudomonadota) and Acidobacteria (Acidobacteriota) at the late afforestation stages. Our findings provide a first contribution to clarify how fungi and bacteria respond to spontaneous afforestation. This is particularly relevant in the context of climate change mitigation, considering the fundamental role of microorganisms in shaping soil carbon storage dynamics
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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